FIG. 1 is a block diagram of an example prior art magnetic disk drive system 100 having a head-disk assembly 104 and a hard disk control system 108. The hard-disk assembly 104 includes one or more magnetic disks 112 and one or more corresponding magnetic heads 116 on a moving arm 120. The moving arm 120 may be coupled to an actuator 124 that may be used to position the magnetic heads 116 over the magnetic disks 112. The hard disk control system 108 includes an interface 128 that receives data to be written to the one or more magnetic disks 112 and transmits data read from the one or more magnetic disks 112. The interface 128 may be communicatively coupled to a microprocessor of a computing system such as a server, a personal computer, a personal digital assistant (PDA), etc., or of a consumer electronics device such as a cellular phone, a set top box, a gaming system, etc., to allow the microprocessor to store data to and read data from the one or more magnetic disks 112. The interface 128 may be coupled to a hard disk controller (HDC) 132. The HDC 132 is in turn coupled to a read/write channel device (RWC) 136 and an actuator controller 140. The RWC 136 is coupled to the magnetic heads 116 and the actuator controller 140 is coupled to the actuator 124. Additionally, the RWC 136 may be coupled to the actuator controller 140. The RWC 136 may include a read channel device.
Data to be written to the disks 112 are received via the interface 128. The HDC 132 transmits signals to the actuator controller 140 indicating the disk and the track on which data is to be written. During positioning, the RWC 136 reads position signal information from the appropriate disk 112 and provides this position signal information to the actuator controller 140. The actuator controller 140 uses the position signal information from the RWC 136 to accurately position the appropriate magnetic head 116 to the desired track. Meanwhile, the HDC 132 will provide the data to be written to the RWC 136. Once the magnetic heads 116 are appropriately positioned, the RWC 136 generates an analog write signal and provides it to the appropriate magnetic head 116 such that the data is magnetically stored on the disk 112 at the desired position.
When data is to be read from one of the disks 112, the microprocessor of the computing device or consumer electronics device provides a request to the interface 128, indicating the data to be read. The interface 128 provides the indication to the HDC 132. Then, the HDC 132 transmits signals to the actuator controller 140 indicating the disk and the track from which data is to be read. During positioning, the RWC 136 generates position signals based on position information written on the disk 112 and provides these position signals to the actuator controller 140. The actuator controller 140 uses the position signals to accurately position the magnetic head 116 to a center of a desired track. Additionally, the HDC 132 indicates to the RWC 136 from which of the disks 112 (if there are multiple disks) to read and when to begin reading so that data from an appropriate portion on the disk 112 will be read. In response, at the appropriate time, the RWC 136 generates a digital signal from an analog signal received from the magnetic head 116. This digital signal is provided to the HDC 132. The HDC 132 provides the retrieved data to the interface 128, which in turn provides it to the requesting microprocessor.
FIG. 2 is an illustration of an example magnetic media disk 150 that may be utilized in the disk drive system 100 of FIG. 1. The disk 150 includes a plurality of servo field areas 154 that generally radiate outwardly from the center of the disk 150. Each servo field area 154 is generally wedge shaped. Additionally, the disk 150 is generally partitioned into a plurality of concentric regions referred to as tracks 158. A servo field area 154 within a particular track 158 may be referred to as a servo mark. Each servo mark may include data which is pre-written on the disk 150 during manufacturing, and such data may include data concerning the location of the servo mark on the disk 150, such as the particular servo field area to which it corresponds and the track in which it is located. As can be seen in FIG. 2, each track 158 will include several servo marks. The servo mark data may be used by the hard disk system to position the magnetic head 116 during read and write operations. Data to be stored is written in the tracks 158 between the servo fields.
FIG. 3 is a diagram illustrating an example format of a servo mark 174. The servo mark 174 includes a pad field 178 that may include data used by the disk drive system for timing adjustment. The servo mark 174 may also include a phase-locked loop (PLL) and automatic gain control (AGC) field 180. The PLL/AGC field 180 includes a pattern which is used by the RWC 136 to synchronize a PLL of the RWC 136. Additionally, the PLL/AGC field 180 includes a pattern which is used by the RWC 136 to adjust an AGC module of the RWC 136.
The servo mark 174 also includes a servo address mark (SAM) field 182 and a track ID field 184. The SAM field 182 and the track ID field 184 each include a pattern indicative of digital data. For example, the SAM field 182 includes data indicative of the servo field to which the servo mark 174 corresponds. Similarly, the track ID field 184 includes data indicative of the track to which the servo mark 174 corresponds. The actuator controller 140 may utilize the track ID field 184 in positioning the magnetic head 116 over the desired track. For instance, signals generated as the magnetic head 116 moves over the track ID field 184 may indicate to the actuator controller 140 the track over which the magnetic head 116 is currently located.
The servo mark 174 further includes a second pad field 186, a first position signal (PS1) field 188, a third pad field 190, and a second position signal (PS2) field (PS2) 192. The PS1 field 188 and the PS2 field 192 include one or more patterns that, when the magnetic head 116 passes over, causes a signal indicative of a position of the magnetic head 116 within the track to be generated. Such signals may be used by the actuator controller 140 as feedback to more accurately position the magnetic head 116 over the center of the desired track.
FIG. 4 is an illustration of a portion of an example position signal (PS) field 200 within a track of a disk. The PS field 200 may be used for the PS1 field 188 and/or the PS2 field 192 in FIG. 3. The PS field 200 includes a first burst 204 and a second burst 208. The alternate black and shaded strips in FIG. 4 represent opposite magnetization states of the media. At least a portion of the first burst 204 is located within the track (it may extend into an adjacent track, for example) but it does not span the entire width of the track. Similarly, at least a portion of the second burst 208 is located within the track but does not span the entire width of the track. Additionally, the burst 204 is at a different radial position (or “cross-track position”) within the track as compared to the radial position of the burst 208. Further, the burst 204 is at a different circumferential position (or “down track position”) within the servo mark as compared to the circumferential position of the burst 208.
As the magnetic head 212 passes over the track in the down track direction, the magnetic head 212 passing over the burst patterns 204 and 208 will result in signals being generated. For instance, a signal corresponding to the burst 204 first will be generated, and then a signal corresponding to the burst 208 will be generated. The generated signals (hereinafter referred to as “position error signals”) will vary depending upon the radial position of the magnetic head 212 within the track. A position estimate generator (a component of the read/write channel 136, for example) may analyze these signals to deduce the position of the magnetic head 116 within the track. The position estimate may be proved to the actuator controller 140, which may adjust the position of the magnetic head 116 based on the position estimate to more accurately position the magnetic head 116 over the center of the track. Patterns, such as the burst patterns 204 and 208, can be of various types such as amplitude patterns, null patterns, phase patterns, orthogonal patterns, dual frequency patterns, etc.
FIG. 5 is a block diagram of a prior art position estimate generator 250. The position estimate generator 250 includes an analog-to-digital converter (ADC) 254 that generates digital samples of the position error signals (PES). A PES demodulator 258 is coupled to an output of the ADC 254 and demodulates the digitized PES. Various techniques for PES demodulation may be employed, and the technique used may depend on the type of patterns employed.
For example, with a null-type pattern, a first magnetization pattern on one side of a centerline of a track is written 180° degrees out-of-phase with a second magnetization pattern on the other side of the centerline. When the magnetization head is directly straddling the track centerline, a PES signal corresponding to the first pattern should have an amplitude equal to an amplitude of a PES signal corresponding to the second pattern. If the head is off-center toward the first pattern, the amplitude corresponding to the first pattern will be larger than the amplitude corresponding to the second pattern. Similarly, if the head is off-center toward the second pattern, the amplitude corresponding to the second pattern will be larger than the amplitude corresponding to the first pattern. By determining the amplitudes of the signals corresponding to the first and second patterns, and then subtracting the amplitudes, a position estimate can be generated. For instance, the magnitude of the position estimate will indicate an approximate distance of the head from the centerline, with a zero value indicating a position on the centerline. Additionally, a sign of the position estimate indicates a direction of displacement from the centerline. The position estimate may be expressed as:
                    Position_Estimate        =                                            α              A                        -                          α              B                                                          α              A                        +                          α              B                                                          (                  Equ          .                                          ⁢          1                )            where aA and aB represent estimated signal amplitudes corresponding to the burst 204 and the burst 208, respectively.
Thus, referring to FIG. 5, the PES demodulator 258 may determine amplitudes of signals corresponding to position patterns in a servo mark, for example. A position estimator 262 may receive the amplitude estimates determined by the PES demodulator 258 and may generate a position estimate based on the amplitude estimates. For example, the position estimator 262 may generate a position estimate according to Equ. 1.